This application claims the priority of German application 197 10 671.4, filed Mar. 14, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a process for producing a component which is made, in regions, of a ceramic-metal composite material, in which process a porous sacrificial body is produced from ceramic precursors, the sacrificial body is filled with softened metal and/or a metallic alloy (hereinafter referred to as filling metal) at a predeterminable filling temperature at or above the softening temperature of the metal and under super-atmospheric pressure. The sacrificial body filled with the metal is heated to or above a reaction temperature which is higher than the filling temperature, and a reaction between the filling metal and the metal of the ceramic of the sacrificial body is carried out at or above the reaction temperature. In this reaction, the ceramic-metal composite material comprising a ceramic phase and a metallic phase is formed, where the ceramic phase comprises CMe.sub.m B.sub.x and/or CMe.sub.n C.sub.y and/or CMe.sub.o CN and FMe.sub.p O.sub.3 and the metallic phase comprises an intermetallic compound of a metal of the ceramic and a filling metal.
The present invention also relates to a component which, at least in regions, comprises the ceramic-metal composite material formed in the foregoing process.
A German patent application, which is not a prior publication, discloses a process for producing a component comprising a ceramic-metal composite material. A sacrificial body of ceramic precursors is filled with a thermally softened metal, in particular aluminum, and/or with a metallic alloy. The filling temperature is below a reaction temperature at which an exchange reaction between a metal of the ceramic precursors and a metal of the filling metal takes place. After the sacrificial body has been filled as completely as possible, the filled sacrificial body is heated to or above the reaction temperature, as a result of which the reaction just mentioned then takes place. This reaction produces a component in which the ceramic-metal composite material comprises a ceramic phase and a metallic phase comprises an intermetallic compound of the metal of the ceramic and the metal of the filling metal.
As a result of the sacrificial body being filled with a metal softened by heating below a reaction temperature of the metal with the material of the sacrificial body, the ceramic matrix is retained during filling and also during the subsequent reaction between the introduced metal and the material of the sacrificial body. Ideally, the pores of the sacrificial body are completely filled, so that when the substances in question are used in stoichiometric amounts, the component has reacted fully throughout and is free of cracks and channels.
Preferably, the filling metal is aluminum and the metal of the ceramic is titanium, so that after the preferred exchange reaction the ceramic phase comprises TiB.sub.x and/or TiC.sub.y and/or TiCN and Al.sub.2 O.sub.3 and the intermetallic compound of the metallic phase is the high-temperature-resistant TiAl.
The material properties of this ceramic-metal composite material are good. Thus, for example, a ceramic-metal composite material which is produced using aluminum as filling metal (FMe) and Ti as metal of the ceramic sacrificial body (CMe) has a density of 3.4 g/cm.sup.3 ; this density is slightly higher than that of the MMCs (metal matrix composites) but is only 42% of the density of comparable cast iron. Particularly in the preferred embodiment, in which the high-temperature-resistant compound is in the form of the intermetallic compound TiAl, the use range of the component extends to at least 800.degree. C., significantly above the values for grey cast iron.
The ceramic-metal composite material produced is used, in particular, to manufacture friction rings for the frictional surfaces of disc brakes. These friction rings are subsequently fixed by mechanical joining techniques such as screws, etc., to the hub of the brake disc.
It is an object of the present invention to further improve the foregoing process so that components comprising a previously known ceramic-metal composite material can be produced more simply, more quickly and, in particular, more cheaply.
This object has been achieved in a process according to the present invention by providing that the sacrificial body is laid into a pressure casting tool in a defined position and fixed in position relative to the pressure casting tool and so as to fill the pressure casting mold except for intermediate regions which are free of the sacrificial body, during pressure casting of the component, the sacrificial body is filled with the filling metal, and by means of the pressure casting tool, a shape which is at least close to the final shape of the component, comprising filled sacrificial body and the intermediate element (s) free of the sacrificial body, is cast. The component after casting is complete is heated to or above the reaction temperature in the region of the filled sacrificial body.
As a result of the pressure casting of the entire component simultaneously with the filling of the sacrificial body, i.e. the region of the sacrificial body and the intermediate elements free of the sacrificial body, in the same pressure casting tool, the subsequent mechanical joining of the individual regions of the component which has hitherto taken place can be omitted.